Olivia, ubuntu-desktop is actually a package used by Gaim; the desktop environment is Gnome (or KDE, or xfce, depending on which flavor Ubuntu you are running and how much you’ve customized). It is perfectly safe to uninstall ubuntu-desktop.

On a completely different note, it is worth mentioning that unless you have the packages tcl8.4 and tk8.4 installed the dpkg-i will fail (both required packages are in the standard repositories and available in synaptic).